An electric load is customarily supplied with a constant voltage by an electric power supply module. The power supply module often has to act as a voltage source. In practice the power supply module supplies the load with a DC voltage V.sub.0 which is maintained constant by means of a feedback loop.
It is often desirable to neutralize a failure of this power supply module by utilizing at least one second power supply module which is identical and mounted in a redundant configuration, i.e. in this case mounted in parallel, with the first power supply module, with respect to the load.
In the latter situation, assuming that two power supply modules are used, it is necessary to prevent unbalanced operation of these two modules from disturbing the supply voltage for the load and from aggrevating the unbalanced operation of the modules. Notably when one of the modules is deactivated, accidentally or voluntarily, the feeding of the load should not be disturbed, but remain ensured by the second module. This problem can be mitigated by connecting a diode, referred to as a blocking diode, to the output of each module, the cathode thereof being connected to the power supply input of the load which carries the voltage V.sub.0. This step is known notably from the document JP-A-1-23724.
At this stage another problem occurs in respect of supplying the load with the DC voltage V.sub.0. Actually, the two power supply modules are assumed to feed the load simultaneously, in the normal mode of operation, so that the feedback loop of each power supply module must be maintained; this is very difficult due to the fact that, the output of the modules being common, downstream from each blocking diode the two feedback loops influence one another to the extent that complex instability and inadmissible pumping phenomena can occur. Moreover, using such an arrangement, in the course of time one of the modules will inevitably feed the load substantially more than the other module, regardless of the precautions taken to ensure suitable symmetry of the construction and balanced control of the modules, each of which has its own reference voltage. One may reach the point where the power supply module with the smallest output, detecting an increasing voltage V.sub.0 (due to the effect of the other module), reduces its voltage V.sub.1, so as to lower V.sub.0, until V.sub.1 =V.sub.0, in which case the blocking diode D.sub.1 is blocked and the voltage V.sub.1 drops to 0, the feedback then being incapable of operating. Should subsequently the module with the largest output fail, the module with the smallest output will start to operate again but, as the voltage V.sub.1 starts from the value 0, there will be a transitory operating phase during which the load is not fed. This transitory phase, even though it is brief, is not admissible. According to the cited document, these problems are solved by introducing, in parallel in the feedback loop, the output signal of a comparator for the anode voltages of the blocking diodes. It is a drawback of this solution that the feedback loops of the two power supply modules influence one another.
It is an object of the invention to provide a voltage source which includes a plurality of power supply modules which are connected in a redundant configuration and where deactivation (voluntary or accidental) of a power supply module does not cause transitory phenomena in feeding the load which affect the load or its operation, and each power supply module remains independent of the others.